The present invention is related to a magnetic recording media which is possible to record large volume information and to a magnetic disk apparatus using this media, particularly suitable to a magnetic recording media and a magnetic disk apparatus for high density magnetic recording.
The requirement for larger capacity to a magnetic disk apparatus is increasing more and more. There are some countermeasures in order to increase the recording density such as (1) improvement of the sensitivity of a reproducing part of a magnetic head, (2) narrower distance between a head element and a recording surface of a magnetic recording media and (3) higher efficiency of a signal processing.
The adoption of a composite magnetic head, which is separated into a recording part and a reproducing part and uses a highly sensitive element utilizing magneto-resistive effect as the reproducing part, is rapidly increased in these years. Recently, a magnetic head utilizing the effect of large variation of magneto-resistance (i.e., giant magneto-resistive effect, or spin valve effect) of a stacked type magnetic layer, which is a stack of plural magnetic layers with non-magnetic layers intervened, is in practical use for the purpose of more improvement of the sensitivity of reproducing part of a head. This utilizes the variation effect of magneto-resistance cased by a relative change of magnetizing direction of plural magnetic layers with non-magnetic layers intervened, forced by a leakage magnetic field from the magnetic recording media.
On the other hand, as important factors to higher recording density of a magnetic recording media, such are listed up as (1) lower noise of a recording media matching to an improved sensitivity of the reproducing part of a magnetic head, (2) more flatness of the surface roughness of a media accompanied by narrower spacing between a head element and the recording film of a magnetic recording media and (3) thinner protective layer.
A longitudinal magnetic recording media using alloy with Co as a main component such as CoNiCr, CoCrTa, CoCrPt, or CoCrPtTa is widely used as a magnetic layer of magnetic recording media. A magnetic layer of Co-alloy containing Pt, particularly, exhibits high coercivity and increases output at high linear recording density region, so that it is suitable for high recording density. These Co-alloys conform to hexagonal closed packed construction with c axis as easy axis of magnetization, so it is preferred that c axis is directed longitudinally for the application of longitudinal magnetic recording media. Therefore, there is widely used procedure that the under layer of body centered cubic construction is formed first on a substrate, then Co-alloy magnetic layer is formed on it by epitaxial growth, thus c axis is directed longitudinally.
Conventionally, Cr has been used as under layer. But in case that large atoms as Pt, etc. are contained in the magnetic layer, a method of making c axis orient crystallographically parallel to the film surface is proposed (JP-A-NO.63-197018, JP-A-No.62-257618) by improving lattice matching between magnetic layer and under layer, using Cr-alloy whose lattice space is increased by adding Ti (JP-A-No.63-197018) or V (JP-A-NO.62-257618) to Cr. As for under layer materials other than these, it is disclosed by JP-A-No.63-187416 that a wide variety of materials including Mo, W, Hf, and so on are usable. And as disclosed by JP-B-No.10-143865, it is shown that media noise can be stably decreased by forming amorphous alloy layer containing Cr or Zr of highly oxidization tendency, in addition to Co as the main component, between Cr-alloy under layer as described above and a substrate, and by slightly oxidizing the surface by exposing the surface in oxygen atmosphere.
The following is proposed as a technology to improve reliability against contact of magnetic head and magnetic recording media. That is, preferable surface structure of magnetic recording media is proposed by JP-B-No.5-114127 and JP-B-No.8-297834 concerning wear reliability, which is suitable to preventing head crash and media damage mainly occurred by CSS (Contact Start Stop) at starting or stopping of an apparatus. And the media surface is proposed by JP-B-No.11-232638 to prevent contact of head and media. JP-B-No.7-95369 proposes a method applying projection on the media surface in order to improve wear reliability of a flexible disk using a contact type head.
In addition, a method to retract a magnetic head out of the media at stopping of the media rotation is disclosed by JP-B-No.11-110933 in order to reduce the media surface roughness accompanied by narrower flying height of the head and prevent adhesive problem of a magnetic head at stopping at the same time.
It became possible by the above prior art to prevent from adhesive problem of a head on the magnetic media and to decrease media noise caused by higher playback sensitivity of the magnetic head. However, the spacing is getting narrower rapidly in these days to achieve higher recording density, so that the head and media interface is becoming difficult to prevent a head from contact with the media even during recording or reproducing operation. Therefore, it is required for media surface to minimize the spacing loss and besides realize high wear reliability.
The first purpose of the present invention is to present a high wear reliable magnetic media with low friction even under such a condition of low glide height as described above in conjunction with low noise characteristics which is important to achieve high recording density. The second purpose is to present a highly reliable and large capacity magnetic storage apparatus.
In order to solve the problem described above, various kinds of magnetic recording media were prepared, which were formed of a magnetic alloy layer containing Co as the major component on an under layer on a substrate, a protective layer containing C as the major component and a lubricant layer stacked in the order, by changing the structure of the under layer and the surface shape of the media and their characteristics were evaluated. As the result it was found that a good result was obtained and the first purpose described above was achieved when the under layer was formed of plural under layers including first layer of substantial amorphous and second layer of crystalloid laid in that order, and xcex94BH[0.01, 50] defined by |BH[0.01%]xe2x88x92BH[50%]|, which is the difference of the height of BH[0.01%] (i.e., Bearing ratio is 0.01%) and the height of BH[50%] (i.e., Bearing ratio is 50%), was not smaller than 3 nm and not larger than 6 nm in the Bearing Curve given by a surface roughness curve of the magnetic recording media.
By forming substantial amorphous layer as the first under layer, the second under layer of crystalloid formed on the first layer can be of fine crystalloid, and the crystalloid of the magnetic layer formed on it becomes also fine, so that the media noise is decreased. In addition, the growth of abnormally large particles of crystalloid, which are observed during the crystal growth in case of crystalline film, is suppressed by making the first layer be substantial amorphous. Thus, the probability of contact of the slider and the media is decreased when the glide height of a magnetic head slider is reduced, so that both of less media noise and higher reliability are achieved at the same time. The wording of xe2x80x98substantial amorphousxe2x80x99 herein defines the structure which diffraction pattern is observed as halo by a photograph of selected area electron diffraction image by a transmission electron microscope. The microscopic structure of layers constructing this kind of magnetic recording media can be evaluated by observing with a transmission electron microscope with high magnifying power, or by observing the diffraction ring pattern of selected area electron diffraction image, a sample piece thinly sliced in perpendicular direction to the surface of the substrate or a sample piece of the substrate thinned by machine grinding first and then thinned again on the both sides of top and bottom by ion-thinning-method.
CoCrZr, NiCrZr, CoP, NiP and so on can be used as a material composing the first under layer. By using Co or Ni as a main component of the first under layer, high bond strength to the substrate can be obtained. If Cr or P is added as an additional element, the ferromagnetic factor of Co or Ni contained in the first under layer is effectively decreased so that the magnetization of the first under layer can be negligible small to a reproducing head. An alloy containing Ni or Co as a major component, which contains Cr and Zr at the same time, is preferable since it gains particularly high corrosion resistant characteristics by adding Cr, and is very preferable to add furthermore Zr to it since it can make the first under layer be amorphous without degrading corrosion resistance. When P is added, it realizes both of the effective reduction of ferromagnetic factor of Co or Ni and the change to amorphous at the same time. By exposing slightly the surface of CoCrZr, NiCrZr or NiP to oxide atmosphere, the crystalline particles of Cr alloy under layer formed on it can be minute, and the crystallographic orientation can be coincided to (100) orientation which can make c axis of Co alloy be parallel to the film plane. As the result the media noise is reduced stably. Instead of Cr added to the first under layer, adding Ti, V, Mo or Nb also gives equivalent effect to the case of Cr. Moreover, instead of Zr added to the first under layer, adding Ta, Hf, Y or W also gives equivalent effect to the case of Zr. The thickness of the first under layer is preferred to be not smaller than 20 nm and not larger than 80 nm. It becomes easier for a media damage caused by contact with a head to be happened if the thickness of the first layer is less than 30 nm. On the other hand, the thickness larger than 80 nm is not preferable since the efficiency of mass production becomes lower. It is specially preferred that the thickness of the first under layer is not less than 30 nm and not more than 65 nm since it realizes particularly high reliability and high mass production efficiency.
The crystalline structure of the second under layer is preferred to be an nonmagnetic metal of body centered cubic structure. As an example, a thin film of nonmagnetic Cr-base alloy in forms of solid solution of (100) orientation is used, which is expected to be good crystalline matching orientation to a magnetic layer. The (100) orientation herein means crystallographic orientation of (100) plane of crystalloid to be parallel to the substrate plane. As the material of the second under layer, alloy of CrTi, CrTiMo, CrMo or so on can be used. The thickness of the second under layer is preferred to be not less than 3 nm and not larger than 60 nm. It becomes difficult to control crystalline structure and crystallographic orientation of the magnetic layer formed on it if the thickness is less than 3 nm. The thickness is not preferred more than 60 nm since it tends to make abnormal growth of crystalline particles unexpectedly which is an obstructive factor for gliding of a head and degrades mass production efficiency. It is particularly preferred for the thickness of the second under layer to be not less than 15 nm and not larger than 35 nm since low noise and high reliable media against low glide height can be produced efficiently. It is preferred for the density of additive Ti of the second under layer to be not less than 18 at. % and not more than 23 at. % in case of CrTi alloy as second under layer. If the density of Ti as an additive within said second under layer of CrTi alloy is less than 18 at. %, the crystalline matching to the magnetic layer is decreased. It is not preferred that the density of Ti as an additive is greater than 23 at. %, on the other hand, since the size of crystalline particles of the under lager and that of the magnetic layer, continuously formed on the under layer, becomes large so that media noise increases.
When xcex94BH[0.01, 50] defined by |BH[0.01%]xe2x88x92BH[50%]|, which is the difference of the height of BH[0.01%] (i.e., Bearing ratio is 0.01%) and the height of BH[50%] (i.e., Bearing ratio is 50%), is not smaller than 3 nm and not larger than 6 nm in the Bearing Curve given by a curve of the surface roughness of the magnetic media, the friction at contact of head slider and media is suppressed in low so that higher wear reliability is achieved. It is particularly preferred that the surface structure of the media forming substantial amorphous layer as the first under layer meets the condition as described above since all the characteristics of low noise, low glide height and high reliability are achieved simultaneously. xcex94BH[0.01, 50] less than 3 nm increases the friction at contact of head and media and shortens the life under the continuous sliding wear test. In addition, the head vibrates in pitching axis causing unstable recording and reproducing, therefore it is not preferable. It is not preferred that xcex94BH[0.01, 50] exceeds 6 nm, on the contrary, since the spacing between head slider and media can not be reduced enough to achieve high recording density beyond 10 gigabits per square inch. It is preferable figure to achieve high wear reliability that xcex94BH[0.01, 50] is not less than 3 nm and not more than 6 nm, and xcex94BH[0.0 1, 0.8] defined by |BH[0.01%]xe2x88x92BH[0.8%]|, which is the difference of the height BH[0.01%] (i.e., Bearing ratio is 0.01%) and the height BH[0.8%] (i.e., Bearing ratio is 0.8%), is not more than 3 nm. It is not preferable that xcex94BH[0.01, 0.8] exceeds 3 nm since the life under continuous sliding wear test is shortened. In order to improve higher reliability against continuous contact of head slider and media, the following condition is preferred. That is:
where the difference between the height BH[1%] (i.e., Bearing ratio is 1%) and the height BH[50%] (i.e., Bearing ratio is 50%), in Bearing Curve given by the surface roughness curve of media, is defined as y (=|BH[1%]=BH[50%]|), and
the difference between the height BH[15%] (i.e., Bearing ratio is 15%) and the height BH[50%] (i.e., Bearing ratio is 50%) is defined as x (=|BH[15%] BH[50%]xe2x88x92BH[50%]|); then,
the point expressed as coordinates (x, y) is within the area surrounded by a segment between point (0.1, 1.6) and point (1, 3), a segment between point (1, 3) and point (1, 4), a segment between point (1, 4) and point (0.1, 4) and a segment between point (0.1, 4) and point (0.1, 1.6) on xy coordinate plane, and
mathematical average of the roughness (Ra) is not more than 0.7 nm.
The life under continuous sliding wear test becomes shorter by one order or worse under the condition out of the area described above.
In order to achieve higher recording density than 20 gigabits per square inch, xcex94BH[0.01, 50] is preferred to be not less than 3 nm and not more than 4 nm for reducing the glide height.
Bearing Curve herein means the Bearing Curve advocated by Abbot, and Bearing ratio means a ratio of the length of the Bearing shown by Japanese Industrial Standard (JIS B 0601) (Reference document: page 23 of xe2x80x98Tribologyxe2x80x99 by co-writer of Yamamoto and Kaneda, published by Rikougakusha). Mathematical average of roughness is in accordance with the expression written in Japanese Industrial Standard (JIS B 0601).
As a forming method of the surface of magnetic recording media described above, it is preferred to form the surface shape so as xcex94BH[0.01, 50] is not less than 3 nm and not more than 6 nm by machining or by chemical surface processing on the surface of a substrate. As for other forming methods of the surface, there is a method which makes low melting point metal like Al grow in island-shaped by sputtering method or a method which makes the protective layer uneven by etching the protective layer by Ar with masking by micro particles sprayed over the surface of it. However, these two methods have demerit as follows. That is, the method, which makes low melting point metal like Al grow in island-shaped by sputtering method, lacks reliability from wear resistant point of view since the low melting point material to form unevenness on the protective layer is low in hardness and Young""s modulus and is easily deformed in general. And the method requires the best suited under layer in order to make low melting point material grow in island-shaped with the most suitable height and density so that it is required to add two spattering processes, then it becomes difficult to keep film-forming process stable and to control it. The method which makes the protective layer uneven by etching the protective layer by Ar, etc. can not avoid cohesion of micro particles used as a mask, so that such cohesion makes large area of projection. The frictional sliding distance becomes long which causes high frictional heat when a head runs through such the large size of projection, therefore it is not preferable because of large playback noise caused. On the other hand, the method to form shape is possible to use wet process in basic to form desired shape of the surface of substrate, which reduces the cost comparing to dry process mentioned above. It is also possible to overcome such two drawbacks as described above and to achieve stable mass production of magnetic recording media. Substrate of tempered glass like Alumino-silicate, Soda-lime, etc. is suitable to the substrate to form mentioned surface shape, however, it is not limited as far as forming such shape as described above is possible.
As the magnetic layer, it is preferred to use a magnetic film which density of cobalt and gold is not more than 80% within composing elements and which coercive force is not less than 240 kA/m when it is measured by a vibrating sample magnetometer applying 800 kA/m of magnetic field to the film plane at room temperature. This is because it has good electromagnetic characteristics in high recording density area. However, the overwrite characteristics is degraded when the coercivity exceeds 400 kA/m, so that the coercivity of media is preferred to be within the value which is controllable keeping overwrite capability. It may also apply an under layer of Crxe2x80x94Mo etc. between said second under layer and the magnetic layer.
For improving wear reliability, it is preferred to apply 3 nm to 12 nm thick protective layer of carbon as a main component on the magnetic layer, and to apply a lubricant layer of 0.5 nm to 3 nm thickness of adsorptive material like perfluoro polyether, etc. on the surface again.
The second purpose of the present invention is achieved by the following manner. As to a magnetic recording apparatus, comprising magnetic recording media, a drive part driving said magnetic recording media, magnetic heads comprising recording part and reproducing part, means to move said magnetic heads relatively against the magnetic recording media mentioned above, mechanical part to make the heads ramp, input means of signal to said magnetic heads, and recording and reproducing signal processing means to reproduce the output signal from said magnetic heads, the reproducing part of the magnetic heads comprises plural electro-conductive magnetic layers which make big resistance change due to relative change of magnetizing direction of external magnetic field and a magneto-resistive sensor containing an electro-conductive nonmagnetic layer placed between said electro-conductive magnetic layers, and the above magnetic recording media in accordance with the present invention is used as the magnetic recording media.
As said magneto-resistive effect head, it is preferred to form the magneto-resistive sensor between two shield layers of soft magnetic material displaced to each other layer by from not less than 0.06 micron to not more than 0.18 micron. The output cannot be obtained enough in the high recording density area beyond 500 kFCI if the distance of the shield layers is greater than 0.18 micron. And it becomes not easy to keep enough insulation between the shield layer and the magneto-resistive sensor if the distance of the shield layers is less than 0.06 micron. It is preferred that the product (Brxc3x97t), where t is the thickness of said magnetic recording media, and remanent magnetization flux density Br, where Br is measured applying magnetic field along to the relative moving direction of the magnetic head against the magnetic recording media, is not less than 3.2 mA (40 Gauss-micron) and not more than 6.4 mA (80 Gauss-micron). It increases the danger to reproduce wrong information by degradation of reproducing output being left long time after being recorded if Brxc3x97t is less than 3.2 mA (40 Gauss-micron). It becomes difficult to overwrite at recording if Brxc3x97t exceeds 6.4 mA (80 Gauss-micron).
As for the magnetic recording apparatus described, the reproducing part of the magnetic head is preferred to use plural electro-conductive magnetic layers, which make big resistance change due to relative change of magnetizing direction by external magnetic field, and a magneto-resistive sensor containing an electro-conductive nonmagnetic layer, placed between said electro-conductive magnetic layers, in order to get stable read-back signal recorded at maximum linear recording density over 400 kFCI. In addition, the structure of the magnetic head is preferred so as that the glide height is not more than 13 nm, the area of the surfaces of glide rails is not larger than 1.4 square millimeter, and that the mass of the slider is not more than 2 mg. According to this, it is achieved that the possibility of a crash of the magnetic head to said projection is reduced and, at the same time, the energy at a crash can be small, so that both of high recording density more than 11 gigabits per square inch and high reliability against a crash are achieved.